Sandwich panel construction



May 21, 1963 R. A. ANDERSON ETAL 3,090,212 SANDWICH PANEL CONSTRUCTIONFiled Sept. 27, 1961 2 Sheets-Sheet 1 FIG. I

INVENTORS ROGER A. ANDERSON ROBERT T. SWANN I v ATTOR YS y 1963 R. A.ANDERSON ETAL 3,090,212

SANDWICH PANEL CONSTRUCTION Filed Sept. 27, 1961 2 Sheets-Sheet 2 FIG. 3

INVENTORS ROGER A. ANDERSON ROBERT T. SWANN BY jw/ 9' M. m; YS

United States Patent 3,090,212 SANDWECH PANEL CONSTRUCTIQN Roger A.Anderson, Newport News, and Robert T. Swarm,

Hampton, Va, assignors to the United States of America as represented bythe Administrator of the National Aeronautics and Space AdministrationFiled Sept. 27, 1961, Ser. No. 141,229 12 Claims. (Cl. 62-467) (Grantedunder Title 35, U.S. Code (1952), see. 266) The invention describedherein may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentof any royalties thereon or therefor.

This invention relates generally to a system for the re moval of heataccumulating in a heat shield panel or bar rier positioned between anarea of high heat concentration and an area of lower heat concentration,and more particularly to a sandwich panel construction including theprovision of means for maintaining the temperature in the area of lowerheat concentration at a predetermined level independent of the amount ofheat applied to the heat shield in the area of high heat concentration.

It will be appreciated that the sandwich panel construction of thepresent invention is applicable to any type of furnace wallconstruction,heat shield, or the like, where it is desirable to protect an area orspace from excessive temperatures prevailing in an adjoining area orspace, such as, for example, in the protection of various mechanisms orindividuals required to work adjacent areasof excess heat, or inaerospace vehicles adapted to fly at high speeds.

One heretofore proposed system for obtaining these desired resultscalled for the provision in a wall construction of closed looprecirculating systems carrying heat to a water boiler or storage tank.Such a system is conventional in the cooling of stationary furnacewalls, as illustrated by U.S. Patent 2,981,241, to Barton. This priorart system, however, is not considered to be capable of handling theextreme heat loads of the present system, even when the cooling channelsare positioned closely adjacent to each other. In addition, this priorart system relies on conduction in the wall materials to carry heat tothe cooling channels, and thus restricts the choice of materials tothose of high thermal conductivity. The operation of this particularsystem is also sensitive to small leaks, and is quickly disrupted if anyone cooling channel is blocked or ruptured.

Another prior art system for removing heat from a heat barrier structurecontemplates the provision in a panel Wall construction of a waterevaporation system utilizing wicking material for Water stowage withinthe panel wall. Such an evaporation cooling system is illustrated inU.S. Patent No. 2,908,455 to Hoadley and in U.S. Patent No. 2,922,291 toFox et a1. Such a system, however, involves stowage of the water orother coolant in the panel wall, and relies on capillary action in awicking material to distribute coolant over short distances. Stowage isdifficult to accomplish when the coolant requirement is large, andeither requires foreknowledge of the total heat load to be imposed onthe various areas to be cooled or requires that excessive coolant bestowed at all areas to handle heat loads not readily predeterminable bythe designer. This system is further considered impractical for highspeed aerospace vehicles, since a fluid-tight doublewall structurecompartmented into numerous panels would be required to minimizeacceleration force eifects on coolant distribution. Further, amicrometeoroid puncture during the space flight portion of a vehiclemission could lead to serious loss of coolant stowed adjacent thevehicle ace.

3,09 0,2 l 2 Patented May 21, 1963 The present invention combines theadvantageous features of both of the aforementioned prior art systemsWhile minimizing the disadvantages thereof. Accordingly, an object ofthe present invention is the provision of .a new and improved cooledwall panel structure.

Another object of the instant invention is the provision of a new andimproved system for the removal of heat in a wall panel construction.

A further object of the present invention is the provision of heatbarrier means for preventing excessive heat accumulation within :aselected area.

Still another object of the instant invention is the pro vision of animproved form of heat exchange panel structure particularly adapted forthe thermal protection of human life and equipment.

A still further object of the instant invention is the provision of anew and novel fire wall panel construction interpositionable between anarea of high heat concentration and an area of lower heat concentration.

According to the present invention, the foregoing and other objects areattained by providing, in a heat barrier wall, sandwich panel units ofthe type including a corrugated core element. Spray tubes are positionedwithin alternate individual corrugations of the core element, and areadapted to spray water or other liquid coolant onto absorbent wickingmaterial secured to the interior of an external surface portion of thepanel. A heat shield element is operatively coupled with the exterior ofthis external surf-ace portion of the panel and is positionable adjacentan area of high heat concentration. Heat impinging upon the shield leadsto heat accumulation within the panel, causing evaporation of thecoolant in the wicking material, and the evaporated coolant leaves thepanel through exhaust conduits with the result that the temperature atthe other external surface portion of the panel is maintained at orbelow a predetermined level.

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein:

FIG. 1 is a schematic view of a typical heat barrier panel structure ofthe present invention interconnected with a liquid coolant supplysystem;

FIG. 2 is a plan view of the heat barrier .panel structure with partsbroken away to show the interior thereof; and,

FIG. 3 is a cross-sectional elevational view of the heat barrier panelstructure taken along the line 3-3 of FIG. 2.

Referring now more particularly to the drawings, wherein like referencenumerals designate identical parts throughout the several views, andmore particularly to FIG. 1, there is shown a heat barrier or shield 11operatively coupled with a circulatory cooling system. Heat barrier orshield 11 is preferably of metallic construction, although othersuitable conventional materials such, for example, as ceramics or hightemperature resistant plastics, may be utilized as found desirable. Theheat barrier 11 is disposed between an area of high heat concentrationand an area to be thermally protected, i.e., an area of lower heatconcentration. Referring now more particularly to FIGS. 2 and 3, theheat barrier or shield 11 is shown operatively coupled with a sandwichpanel unit including a metallic external wall or skin 12, a metallicinner wall or skin 13, and an intermediate corrugated metallic coreelement generally designated by the reference numeral 14. Core element14 is composed of a unitary sheet metal member including end flangeportions 15, diagonally disposed web portions 16, and intermediateflange portions 17 and 19. Alternate ones of the diagonal web portions16 are parallel to each other and are disposed at approximately 45degree angles to the skins 12 and 13. The Web portions 16 convergingtoward external skin 12 are joined by flange sections 17 adjacent andparallel to external skin 12 and attached thereto by suitable means suchas, for example, rivets 18. The Web portions 16 which converge towardinternal skin 13 are joined by bottom flange sections 19 adjacent andparallel to internal skin 13- and secured thereto by any suitable meanssuch as, for example, welds 21. End flange portions 15 of core element'14 are secured to the skins 12 and 13 by conventional means, such asWelds 2-2 or rivets 18. The space between inner wall or skin 13 andouter wall or skin 12 is thus divided by corrugated core element 14 intoa plurality of longitudinally extending bulkheads forming parallelchannels 24 and 31 which are substantially trapezoidal in cross-section.Rivet means 18 may also be extended through external skin or wall 12 toconnect with shield 11 where so desired.

A plurality of longitudinally disposed spray tubes 25 extend into thesandwich panel unit at spaced intervals. These tubes 25 are attached bysuitable welds or thermosetting adhesives 26 within the minor areaportion of the parallel longitudinally extending channels 24, adjacentinner 'Wall or skin 13, and extend substantially the entire length ofthese channels 24. Each of spray tubes 25 is provided on one surfacethereof with a row or rows of minute, closely spaced holes27 adapted todirect a spray of water or other liquid coolant from the interior of thetube 25 onto absorbent wicking material 28 which, in turn, is fixedlysecured by suitable adhesive or bonding means 29 to the major surfacearea of the internal surface of outer skin or wall 12 spaced from thespray tubes. The alternate channels 31 of corrugated core element 14-not occupied by spray tubing 25 are utilized as steam exhaust passagesleading through pressure relief valves, not shown, to exhaust conduits32 which, if so desired, may be directed to any desirable point on theexterior surface of heat shield -11 for the cooling of selected exteriorareas of the heat shield. The corrugated core element 14 also isprovided, on alternate ones of diagonal web portions 1s, with meansforming furled holes 3 3 which permit the transfer of steam fromchannels 24 to steam exhaust channels 3 1 while hindering the flow ofwater therethrough. The excess water or other coolant not converted tosteam is thus available for transfer back to a central water reservoir,or may be discarded as waste, as will be explained more completelyhereinafter.

To assemble the above described structure, spray tubes 25 may beadhesively bonded, by any well known thermosetting adhesive 26, orattached in any other suitable manner, to corrugated core element 14which has been previously attached, as by spot welds 21, to the exteriorside of inner skin or wall 13. Wicking material 28 is secured, bysuitable bonding means 29,.to the interior side of outer skin 12, whichmay then be fastened to corrugated structure 14 by rivets .18 or anyother suitable equivalent means. The assembled structure may then bepositioned adjacent heat shield 11, which may be a separate structureor; as in furnace walls or stationary fire shields, may be assembleddirectly on and attached to the sandwich panel. It will readily be seenthat a complete cooling system checkout may be accomplished prior toassembly of the outer wall to the corrugated structure and prior to theapplication of the heat shield to the outer skin.

In operation of the system, referring once again to FIG. 1, Water orother liquid coolant is admitted through a valve 34, which may 'beactuated manually, or automatically by means responsive to temperature,motion or time control, from a pressurized central coolant supplyreservoir 35, into inlet coolant supply manifold 36 and thence intospray tubes 25. Obviously, the temperature of heat shield 11 when valve-34 opens would be somewhat higher than the maximum temperature to bemaintained along internal wall or skin 13. The Water or other coolant isforced through inlet supply manifold 36, spray tubing 25,

and onto wicking material 28. As the temperature of wicking material 28increases due to heat emanating from heat shield 11, the water isevaporated and converted into steam which results in convective coolingof heat shield 11 and the maintenance of a maximum temperature level forinternal Wall or skin 13 by disposing of heat as collected on heatshield 11.. The amount of Water forced into the cooling area ispredetermined by the total heat load expected for the panel and, ofcourse, varies with the size and shape of the panel and the amount ofheat applied to shield 11. The system is calibrated to assure that atleast the minimum amount of water required to maintain the desiredtemperature level reaches the cooling area. Any excess water is returnedto outlet coolant return manifold 37, through return tubes 39, and maybe pumped back into central reservoir 35 by a suitable conventional pump38. Steam created by the heating of the water coolant helps maintain thedesired temperature level of inner skin 13 and is exhausted throughsteam exhaust ports 32 to the exterior of the system. It is alsocontemplated that this exhaust steam can be directed to selectedexterior areas of heat shield 11 for mass transfer cooling thereof, ifso desired. It is further within the scope of this invention that anyconventional source of water or other liquid coolant under pressure maybe connected to supply manifold 36, and that excess coolant from returnmanifold 37 may be discarded as waste when so desired.

From the foregoing description, it will be readily apparent that thepresent invention may be employed as a cooling system for any type ofarea where it is desirable that the temperature level adjacent internalWall or skin 13 be maintained below a predetermined maximum. Under thesystem of the present invention, using water as the coolant, it has beenfound possible to provide heat barriers capable of disposing of heat atrates from 0-5 B.t.u.s/ft. -sec. with a capability in localized areas(about 1 in?) of 20 B.t.u./ft. -sec., and the system as thus designedprovides a positive temperature cut-off at degrees F. for inner wall 13independent of the timewise and spatial distribution of heat applied toheat shield 11. Although this temperature may be uncomfortable to humanswhen endured over a long period of time, no difiiculty is experienced byindividuals at this temperature level during relative short intervals oftime. Further, even protracted exposure of instruments, mechanisms, orthe like to such temperature levels is not expected to result indeleterious effects thereon.

Whereas the operation of the device according to the present inventionhas been described in connection with a specific structural panelbarrier utilizing Water as a coolant, it is not so limited and the useof any liquid coolant is contemplated, while the structure may vary fromfire shields for individuals to entire building or vehicle coolingsystems.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A sandwich panel heat barrier structure, comprising: an internalskin, an external skin spaced from said internal skin, a core elementincluding a plurality of bulkheads disposed intermediate said internaland external skins and attached thereto to divide the space between saidskins intoa plurality of longitudinally extending channels, absorbentmeans fixedly positioned adjacent the inner surface of said externalskin and a plurality of spray tubes individually secured within at leastsome of said channels and adapted to spray a liquid coolant onto saidabsorbent means.

2. A sandwich panel heat barrier structure, comprising: an internalskin, an external skin spaced from said/ internal skin, a corrugatedcore element disposed intermediate said internal and external skins andattached thereto, absorbent wick material fixedly attached to the innersurface of said external skin over the major portion thereof, and aplurality of spray tubes attached to said corrugated core element atspaced intervals and adapted to spray a liquid coolant onto saidabsorbent wick mate- 3. A sandwich panel heat barrier structureaccording to claim 2 and further including outlet means within saidcorrugated core element for removal of excess coolant from said wickmaterial.

4. A substantially hollow wall panel adapted to be exposed on onesurface thereof to extreme heat, said hollow wall panel comprising atleast an inner skin, an outer skin, and a core element positionedbetween said skin-s, said core element comprising a corrugated metallicsheet secured to said inner and outer skins, absorbent means fixedlyattached to said outer skin and adjacent to said core element, and meansto continuously supply a liquid coolant to said absorbent means toeffect cooling of said outer skin.

5. A wall panel according to claim 4 wherein the space between saidinner and outer skins is divided into a plurality of longitudinallyextending channels by said core element.

6. A wall panel according to claim 5 wherein said absorbent means andsaid means supplying liquid coolant thereto are both positioned withinalternate ones of said longitudinally extending channels.

7. A system for disposing of heat accumulating in a heat barrier adaptedto be positioned between an area of high heat concentration and an areaof lower heat concentration, comprising in combination a heat shield; asandwich panel structure; said panel structure including, an externalskin attached to said heat shield, an internal skin, and a corrugatedcore element disposed intermediate said internal and external skins andsecured thereto at spaced intervals; said core element defining aplurality of longitudinally disposed channels between said internal andexternal skins, tubular spray means within alternate ones of saidchannels extending substantially the entire length of the respectivechannel, and a supply manifold disposed externally of said sandwichpanel structure and connected to a central coolant supply reservoir andto each of said tubular spray means for the transfer of coolant fromsaid reservoir to said tubular spray means.

8. A heat protective system for use between an area of high heatconcentration and an area of lower heat concentration comprising heatshield means adjacent the area of high heat concentration, a sandwichpanel cooling construction adjacent said heat shield means, saidsandwich panel construction comprising an inner skin, an outer skin, anda core element, said core element comprising a corrugated metallic sheetsecured between said inner and outer skins and defining a plurality ofequally spaced parallel longitudinally extending channels, firstalternate ones of said channels forming cooling channels and havingfixedly secured therein longitudinally extending tubular means, saidtubular means having at least one row of closely spaced minute holes onone surface thereof, an absorbent wicking material fixedly attached tothe inner surface of said outer skin over the major portion thereof andspaced from said row of holes in each said tubular means, one end ofeach said tubular means being operatively connected to an inlet coolantsupply manifold and the other end of each said tubular means beingsealed and terminating within said cooling channel, means operativelyconnecting each said cooling channels to an outlet return manifold,second alternate ones of said longitudinally extending channelscomprising steam exhaust channels, means providing for fluidcommunication between each of said cooling channels and an adjacentsteam exhaust channel, and exhaust means operatively connected to eachsaid steam exhaust channel, liquid coolant being forced under pressureinto said inlet supply manifold and then through said tubular means,delivered as -a spray through said row of holes in each said tubularmeans onto said wicking material from which it may be evaporated andconverted into steam by heat emanating from said heat shield means, theexcess steam passing from said cooling channels into said steam exhaustchannels and then from said steam exhaust channels through said exhaustmeans to the atmosphere, excess coolant not absorbed by said wick material being received by said outlet return manifold.

9. A heat protective system according to claim 8 further including valvemeans actuatable to permit flow of coolant from a central coolant supplyreservoir into said inlet supply manifold, and pump means associatedwith said outlet return manifold adapted to transfer excess coolant fromsaid return manifold back to said central supply reservoir.

10. A heat protective system according to claim 8 wherein the meansproviding for fluid communication between each of said cooling channelsand the adjacent steam exhaust channel comprises at least one furledhole in said corrugated core element separating each said coolingchannel and said adjacent steam exhaust channel, whereby steam is freelytransferred from said cooling channel to said exhaust channel and theflow of liquid coolant therebetween is obstructed.

11. A heat barrier structure, comprising: an inner skin; an outer skin;spacing means arranged between said skins and attached thereto to retainthem in fixed spaced relation; absorbent means fixedly positioned atspaced points between said skins; and means to direct a spray of liquidcoolant onto said absorbent means.

12. A structure according to claim 11 wherein said spacing means formsbulkheads dividing the space between said skins into a plurality ofcompartments; and said means to direct a spray of liquid coolant ontosaid absorbent means are positioned within selected ones of saidcompartments.

References Cited in the file of this patent UNITED STATES PATENTS2,576,843 Lockman Nov. 27, 1951 3,013,641 Compton Dec. 19, 1961 FOREIGNPATENTS 481,285 Italy May 27, 1953

1. A SANDWICH PANEL HEAT BARRIER STRUCTURE, COMPRISING: AN INTERNALSKIN, AN EXTERNAL SKIN SPACED FROM SAID INTERNAL SKIN, A CORE ELEMENTINCLUDING A PLURALITY OF BULKHEADS DISPOSED INTERMEDIATE SAID INTERNALAND EXTERNAL SKINS AND ATTACHED THERETO TO DIVIDE THE SPACE BETWEEN SAIDSKINS INTO A PLURALITY OF LONGITUDINALLY EXTENDING CHANNELS, ABSORBENTMEANS FIXEDLY POSITIONED ADJACENT